1. Field of the Invention
The invention relates to an electric hand-held power tool that performs a predetermined working operation to a work-piece by means of a tool bit rotationally driven by a motor. Particularly, the invention relates to a technique to detect excessive reaction torque exerted onto the power tool when, for example, the tool bit is inadvertently locked.
2. Description of the Related Art
Japanese non-examined laid-open patent publication 2011-093073 discloses a hammer drill that detects an output torque of an electric motor for driving a tool bit, as well as detects a driving state of a tool body around the tool bit by utilizing an acceleration sensor. According to the known hammer drill, the torque transmission between the electric motor and the tool bit is interrupted when predetermined threshold value is detected in order to prevent an inadvertent rotation of the power tool.
On the other hand, it is desired to provide a more accurate system with respect to a detection of such inadvertent rotation of the power tool.